I will expand on a comment below. Tubes usually distort with even order harmonics which means the distortion is usually in key with the note and our brains find

I will expand on a comment below. Tubes usually distort with even order harmonics which means the distortion is usually in key with the note and our brains find this distortion pleasing. Transistors distort with odd order harmonics which sounds more dissonant and harsh to the ears. Transistors also tend to be clean or clip, there is little to no build up. Tubes saturate gradually and can make things sound "warmer, fuller and generally awesome". Not all tubes are great though and it doesn't look like these are power tubes so it would be for preamp/line level gear only. Either way I'm really excited to see this.